U.S. Pat. Nos. 4,584,439, 4,903,308, 5,127,060, and pending U.S. patent applications Ser. Nos. 07/436,914 filed Nov. 14, 1989, now issued as U.S. Pat. No. 5,198,624; No. 07/730,172 filed Jul. 12, 1991, now issued as U.S. Pat. No. 5,230,021; No. 07/916,038 filed Jul. 17, 1992, No. 07/882,144 filed May 11, 1992, and No. 07/962,988, filed Oct. 15, 1992, are incorporated herein by reference. These references disclose variations and refinements of audio transducers having flexible diaphragms that can be generally described as "cylindrical" in the broadest sense of the term. That is, the diaphragm is defined by a two dimensional cross-sectional profile that is projected on an axis to form a three-dimensional diaphragm having a constant cross section. Typically, this profile is in the form of a "figure-eight" or a "figure-three" shape having two adjacent parallel semi-cylindrical lobes facing forward toward the listener.
In operation, these disclosed transducers generate sound by a "rolling motion" in which an electromagnetic coil attached to the diaphragm interacts with a fixed magnetic field to move in a direction perpendicular to the vertical axis of projection of the diaphragm, oscillating toward and away from the listener in a forward and rearward direction. While the transducers of the above-referenced applications and patents are quite effective, there remains a need for additional improvements to improve performance and reduce manufacturing costs.
Existing transducers have variations in efficiency over the useful frequency range. One variation may be generated by internal reflections of acoustic waves within the diaphragm at the top and bottom free edges of the diaphragm. A loss of efficiency may also occur at the top and bottom free edges of the diaphragm; acoustic pressure generated at the front of the diaphragm may be dissipated by the flow of some air over the edges of the diaphragm to the low-pressure region behind the diaphragm.
A further need in the prior art is to provide a simplified means for centering or positioning the diaphragm relative to the magnet structure during manufacturing. In addition, there is a need to reduce manufacturing costs by reducing the quantity and cost of components, and to reduce the need for precision and skilled labor to perform various manufacturing steps. Also, it is desirable to reduce the size and weight of existing transducers.